Exploring Bismuth Coordination Complexes as Visible-Light Absorbers: Synthesis, Characterization, and Photophysical Properties

Bismuth-based coordination complexes are advantageous over other metal complexes, as bismuth is the heaviest nontoxic element with high spin–orbit coupling and potential optoelectronics applications. Herein, four bismuth halide-based coordination complexes [Bi2Cl6(phen-thio)2] (1), [Bi2Br6(phen-thio)2] (2), [Bi2I6(phen-thio)2] (3), and [Bi2I6(phen-Me)2] (4) were synthesized, characterized, and subjected to detailed photophysical studies. The complexes were characterized by single-crystal X-ray diffraction, powder X-ray diffraction, and NMR studies. Spectroscopic analyses of 1–4 in solutions of different polarities were performed to understand the role of the organic and inorganic components in determining the ground- and excited-state properties of the complexes. The photophysical properties of the complexes were characterized by ground-state absorption, steady-state photoluminescence, microsecond time-resolved photoluminescence, and absorption spectroscopy. Periodic density functional theory (DFT) calculations were performed on the solid-state structures to understand the role of the organic and inorganic parts of the complexes. The studies showed that changing the ancillary ligand from chlorine (Cl) and bromine (Br) to iodine (I) bathochromically shifts the absorption band along with enhancing the absorption coefficient. Also, changing the halides (Cl, Br to I) affects the photoluminescent quantum yields of the ligand-centered (LC) emissive state without markedly affecting the lifetimes. The combined results confirmed that ground-state properties are strongly influenced by the inorganic part, and the lower-energy excited state is LC. This study paves the way to design novel bismuth coordination complexes for optoelectronic applications by rigorously choosing the ligands and bismuth salt.


Single crystal x-ray diffraction data
The diffraction data for complexes 1-4 were collected on a four-circle Agilent SuperNova (Dual Source) single crystal X-ray diffractometer using a micro-focus CuK α X-ray beam (λ = 1.54184Å) and an Atlas CCD plate detector (in case of 1 and 2) or a HyPix-Arc 100 hybrid pixel array detector (in case of 3 and 4).The sample temperatures were controlled with an Oxford Instruments cryojet.All data were processed using the CrysAlis Pro programme package from Rigaku Oxford Diffraction. 1 The crystal structures were solved with the SHELXT programme, 2 used within the Olex2 software suite, 3 and refined by least squares on the basis of F 2 with the SHELXL 4 programme using the ShelXle graphical user interface. 5All non-hydrogen atoms were refined anisotropically by the full-matrix least-squares method.Hydrogen atoms associated with carbon atoms were refined isotropically [U iso (H) = 1.2U eq (C)] in geometrically constrained positions.The F o -F c difference maps were in all cases used to identify disordered thiophen moieties.These disorders were modelled using the SAME similarity restraint command in SHELXL. 4The anisotropic parameters of the disordered thiophen groups were restrained or constrained using the SIMU or EADP commands in SHELXL. 4The crystallographic and refinement parameters of 1−4 are given in Table S1.The asymmetric units of the crystal structures of 1−4 are shown in Figures S13 -S16.

Figure S39. (a)
The µs-TA spectra for complex 1 solution under nitrogen atomsphere with probe delay time from 1-50 µs and excitation density 11 µJ cm -2 .(b)oxygen quenching TA decay for complex 1 solution probing at 500 nm, under nitrogen atomsphere and followed with oxygen.
Figure S40 (a) µs-TA spectra for complex 2 solution under nitrogen atomsphere with prob delay time from 1 -50 µs and excitation density 11 µJ cm-2.(b)oxygen quenchingTA decay for complex 2 solution probing at 500 nm, under the order of notrogen, follwed with oxygen and repeat recovery in nitrogen atomsphere.

Figure S13 .
Figure S13.The asymmetric unit of compound 1.The thermal ellipsoids are drawn at the 50% probability level.Colour scheme: carbon -dark grey, hydrogen -white, bismuth -light grey, chlorine -green, nitrogen -blue, sulfur -yellow.The minor occupancy sites are highlighted in black.

Figure S14 .
Figure S14.The asymmetric unit of compound 2. The thermal ellipsoids are drawn at the 50% probability level.Colour scheme: carbon -dark grey, hydrogen -white, bismuth -light grey, bromine -brown, nitrogen -blue, sulfur -yellow.The minor occupancy sites are highlighted in black.

Figure S15 .
Figure S15.The asymmetric unit of compound 3.The thermal ellipsoids are drawn at the 50% probability level.Colour scheme: carbon -dark grey, hydrogen -white, bismuth -light grey, Iodine -purple, nitrogen -blue, sulfur -yellow.The minor occupancy sites are highlighted in black.

Figure S16 .
Figure S16.The asymmetric unit of compound 4. The thermal ellipsoids are drawn at the 50% probability level.Colour scheme: carbon -dark grey, hydrogen -white, bismuth -light grey, Iodine -purple, nitrogen -blue.

Figure S18 .
Figure S18.The dihedral angle between pyrazine and thiophene rings and the SN interactions of (a) 1, (b) 2, and (c) 3.

Figure S21 . 1 .
Figure S21.The comparison of experimentally collected and simulated PXRD patterns of complex 1.The marked diffractions peaks (*) correspond to impurities in form of reagents and unidentified byproducts in 1.

Figure S22 . 2 .
Figure S22.The comparison of experimentally collected and simulated PXRD patterns of complex 2. The marked diffractions peaks (*) correspond to impurities in form of reagents and unidentified byproducts in 2.

Figure S23 . 3 .
Figure S23.The comparison of experimentally collected and simulated PXRD patterns of complex 3.The marked diffractions peaks (*) correspond to impurities in form of reagents and unidentified byproducts or alternative crystal forms of 3.

Figure S24 .
Figure S24.The comparison of the absortion spectra of BiCl 3 , BiBr 3 , and BiI 3 in (a,b) ACN and (c,d) DMF at 10 M under ambient conditions.

Figure S25 .
Figure S25.The normalized absorption spectra of complexes, and ligand recorded in DMF (a) and ACN (b) at 10 M under ambient conditions.(c) Comparison of normalized absorption spectra recorded in DMF and ACN.

Figure S26 .
Figure S26.The comparison of individual absorption spectra of bismuth salts and complexes (a) 1, (b) 2 and (c) 3 recorded in ACN at concentration of 10 M under ambient conditions.

Figure S27 .
Figure S27.The comparison of individual absorption spectra of bismuth salts and complexes (a) 1, (b) 2 and (c) 3 recorded in DMF at concentration of 10 M under ambient conditions.

Figure S28 .
Figure S28.The concentration dependent absorption spectra of 1 (a, b), 2 (c, d) and L ( e, f) recorded in DMF at concentration of 10 M under ambient conditions.

Figure S29 .
Figure S29.The concentration dependent (a) and normalized (b) absorption spectra of BiI 3 recorded in DMF under ambient conditions.

Figure S30 .
Figure S30.The concentration dependent (a) and normalized (b) absorption spectra of 4 recorded in under ambient conditions.

Figure S31 .
Figure S31.The comparison of normalized absorption spectra of BiI 3 , 3 and 4 recorded under ambient conditions in DMF (a) and ACN (b).

Figure S32 .
Figure S32.The comparison of the photoluminescence emission spectra of 1, 2, 3 and L in solvents of different polarity, THF (a, b), ACN (c, d) and DMF (e, f), at the excitation of 392 nm under ambient conditions (conc.= 10 M).

Figure S34 .
Figure S34.The fluorescence lifetime of the comlexes recored in (a) THF, and (b) ACN under ambient conditions at the excitation of 375.6 nm (conc.= 10 M).

Figure S35 .
Figure S35.The titration study of L with increasing the amount of BiCl 3 and BiBr 3 in (a,c) ACN, and (b, d) DMF respectively at excitation of 392 nm under ambient conditions.

Figure S36 .
Figure S36.The comaprison of the absorption spectra of complexes (a, b) 1, (c, d) 2 and (e, f) 3 with the increase in the amount of water at concentration of 10 M under ambient conditions.

Figure S37 .
Figure S37.The comaprison of the photoluminescence spectra of the complexes (a, b) 1, (c, d) 2 and (e, f) 3 with the increase in the amount of water at the excitation of 375.4 nm (conc.= 10 M) under ambient conditions.

Figure S38 .
Figure S38.The comaprison of the fluorescence lifetimes of complexes (a) 1, (b) 2 and (c) 3 with the increase in the amount of water to DMF at the excitation of 375.4 nm (conc.= 10 M) under ambient conditions.

Table S2 .
Illustrating and comparing the bond distances in complexes 1, 2, and 3.

Table S5 .
Table for fluorescence lifetimes of aggregates for complexes 1, 2, and 3 in DMF and water mixture.